The known gear has the disadvantage of not permitting a further increase of speed, and consequently of the peripheral velocity on account of the limited manufacturing precision of the bevel gears, so that the speed of the finished rolled product is limited and no longer suffices for today's requirements. In order to increase the velocity of the finished rolled product, it has been suggested to utilize pinion gear stages from secondary drive to secondary drive, their gear ratio either being the same in all stages or possibly increasing from stage to stage in rolling direction.
However, the pinions in such gearing arrangements, particularly the last stage in rolling directon, reach such high peripheral velocities that this type of design can hardly be recommended for high speed rolling mills of the described type in view of wear, susceptibility to repair, noise development, heat, vibrations, and other similar reasons. A further disadvantage is that because of the large mass to be moved, the inertia momentum and thus switching time for acceleration or deceleration of the stands become too great, i.e. the installation reacts sluggishly. Theoretically, the peripheral velocities and mass could be reduced by choosing smaller gear diameters. However, this cannot be practiced as the gear diameters are roughly predetermined by the distances between the rolling stands.
As technology of rolling and economy of a rolling mill make it imperative that a continous rolling mill has the highest possible velocity of the rolled product and that, above all, a fast regulation of the number of revolutions is possible, the present invention solves the task of improving the group gear of the initially described rolling mill in such a way that while decreasing the pinion peripheral speeds and the inertia momentum, much higher velocities of the finished product are attained without very high structural expenditures, and at the usual initial number of revolutions. To solve this, the present invention arranges a planetary gear after each bevel gear stage.
Planetary gears offer a variety of advantages over the known pinion or bevel gear arrangements. For example, the peripheral velocities of the individual gears, which may be designed smaller due to power distribution, are much lower which, in turn, results in lower inertia momentum so that much higher speeds are possible at the secondary drive without a damaging increase in speed in the preceding parts. Furthermore, planetary gears may be favorably arranged coaxially, which strongly reduces structural volume. Also, the gear efficiency of planetary gears is much better than that of pinion or bevel gear arrangements. Furthermore, they have an advantage over pinion gear arrangements in that gear ratios which require a two-stage design for pinion gear arrangements, can be realized in one stage in planetary gear arrangements. This reduces the entire gear play, which favorably affects inertia behavior.
A particularly simple and favorable construction results when, according to another feature of the invention, the planetary gear arrangement forms a structural unit with the bevel gear arrangement. In this manner, it is possible to further reduce gear play in the entire train. It is advantageous to arrange one bevel gear directly at the pinion cage. In view of stability and inertia resistance of the gear arrangement, it is also preferable if the sun gear of the planetary gear arrangement is arranged "flying" or cantilevered at the end of the rolling mill shaft outside the bearing therefor facing away from the rollers. In this case the rolling mill shaft is designed to permit free adjustability of the sun gear.